// factor.c -- uses loops and recursion to valculate factorials
#include <stdio.h>
long fact(int n);
long rfact(int n);
int main(void) {
  int num;

  printf("This program calculates factorials.\n");
  printf("Enter a value in the range 0-12 (q to quit):\n");
  while (scanf("%d", &num) == 1) {
    if (num < 0)
      printf("No negative numbers, please.\n");
    else if (num > 12)
      printf("Keep input under 13.\n");
    else {
      printf("loop: %d factorials = %ld\n", num, fact(num));
      printf("recursion: %d factorials = %ld\n", num, rfact(num));
    }
    printf("Enter a value in the range 0-12 (q to quit):\n");
  }

  printf("Bye.\n");

  return 0;
}

long fact(int n)  // loop-based function
{
  long ans;

  for (ans = 1; n > 1; n--) ans *= n;

  return ans;
}

long rfact(int n)  // recursive function
{
  long ans;
  if (n > 0)
    ans = n * rfact(n - 1);
  else
    ans = 1;

  return ans;
}
